Paley’s Natural Theology though not by any means an epoch-making may perhaps be called an epoch-marking book. It was the crown of the endeavour of eighteenth-century religious philosophy to found a theology on the evidences of external nature. According to such exact knowledge of Nature’s operations as was then generally available, Paley’s attempt might well be thought to have succeeded. He opens his argument with a striking and effective illustration. He imagines a wayfarer crossing a heath who strikes his foot against a stone, and who asks himself how it came into being. Paley thinks he might be content with vaguely supposing that it was there ‘always.’ But suppose that what he had found at his foot was not a stone but a watch and that he now saw such an instrument for the first time. He would then certainly have not been so easily contented with an answer to the riddle of its existence. He would, if he examined it minutely, have observed that it was a structure intended for a certain purpose, and having all its parts arranged for that object, and mutually interdependent The different substances of which it was composed would be discovered to have each its special appropriateness for the fulfilling of some particular function in the economy of the whole. Though unacquainted with watches he would, if he was a man of sense and cultivation, infallibly conclude that he had before him an instrument intelligently constructed with a certain object in view—the object of measuring the flight of time. He would feel assured of this, even though he should find that the object of the mechanism were not attained with absolute accuracy, and even though there were some parts of it whose functions were not clear to him. The watch would be rightly regarded as a work of design; and the observer would be justified in arguing from it to the existence of a designer, endowed with the faculties of intelligence and conscious purpose, by whom the watch must have been put together.